Currently, resonance devices manufactured using micro-electromechanical systems (MEMS) technology have been used as, for example, timing devices. Conventional resonance devices are mounted onto printed wiring boards, which are incorporated into electronic devices such as smartphones. Such a resonance device includes a lower substrate, an upper substrate that defines a cavity between the lower substrate and the upper substrate. Moreover, a resonator is disposed in the cavity between the lower substrate and the upper substrate.
Generally, the conventional resonator includes a base portion extending in the cavity, which is formed between the lower substrate and the upper substrate, and a plurality of vibration arms extending in parallel to one another in the cavity, each of the plurality of vibration arms having a fixed end, which is connected to an end of the base portion, and a free end. Moreover, each of the vibration arms vibrates in the vertical direction toward the lower substrate or the upper substrate in accordance with the orientation of the electric field applied thereto. For example, in a resonator that includes three vibration arms, electric fields oriented in opposite directions are respectively applied to the center vibration arm and the outer vibration arms, and the center vibration arm and the outer vibration arms vibrate with opposite phases.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-204240.
With the recent reduction in the sizes of electronic devices, there has been a demand for a reduction in the sizes of resonance devices, and thus, there is a need to realize a reduction in the size of a resonance device by, for example, reducing the thickness of the resonance device defined by the above-mentioned vertical direction. Accordingly, in order to reduce the thickness of the resonance device while ensuring a sufficient vibration space of the vibration arms, reducing the thicknesses of the lower substrate and the upper substrate may be considered. However, reducing the thicknesses of the substrates leads to a reduction in the rigidity of the substrates. As a result, deformation, such as warpage, may occur in the substrates or that the substrates will break due to an impact generated when an electronic device falls on the ground, for example.